ASNC: Stress agents or exercise for nuclear imaging?

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DENVER—In the current era of nuclear stress testing, a major debate is whether pharmalogical stress testing is comparable with exercise testing. During a presentation Sept. 11 at the 16th annual American Society of Nuclear Cardiology (ASNC) scientific sessions, Brian G. Abbott, MD, medical director of nuclear cardiology at the Rhode Island Cardiology Center in Providence, R.I., said yes, particularly for diagnosing coronary artery disease.

During his talk, Abbott reviewed the available pharmacological stress testing (dipyridamole, adenosine and dobutamine, among others), and highlighted when and how each should be used. While Abbott argued that pharmacological stress agents may work just as well as exercise tests in these patients, he did warn that there may be increased side effects, as patients are now essentially exercising while sitting down.

“With these types of agents, resting flow is maintained in the setting of a stenosis,” Abbott offered. “Once all adenosine receptors are bound there is no ability to increase flow in response to the demand. Therefore, flow is maintained by these adenosine receptors.”

What’s out there?

  • Dipyridamole (marketed as Permole or Persantine): The drug is an indirect coronary vasodilator. Abbott suggested that patients avoid caffeine for 12 hours prior to the test to prevent false-negatives. Additionally, he recommended that the clinician inject the tracer three to five minutes after infusion. Side effects include chest pain and dizziness.
  • Adenosine: This is a direct coronary vasodilator that can result in a 3.5-fold increase in myocardial blood flow. Abbott suggests no caffeine for 12 hours and no dipyridamole for 48 hours. The dose should consist of a 140 mcg/kg/min infusion. Abbott said that a four-minute infusion can also be effective; however, infusion should be continued two minutes post-tracer injection. Side effects are not uncommon and typically include chest tightness.
  • Regadenoson (marketed as Lexiscan): This is a selective A2a adenosine receptor agonist used for pharmacologic stress during radionuclide myocardial perfusion imaging. This can be used in patients undergoing perfusion who are unable to exercise. Contraindications include sinus node dysfunction and second and third AV block.
  • Dobutamine injection: The injection dose increases heart rate, blood pressure and contractility and is indicated for patients who can’t exercise or undergo vasodilator stress.

What works best?

Abbott offered that incorporating low-level exercise in patients undergoing pharmacologic stress testing can help improve outcomes. In fact, he said that it can reduce the side effects of these agents by 30 percent and can also improve diagnostic accuracy.

During the Advanced MPI trial, which enrolled 784 patients, the researchers randomized patients to receive either adenosine or regadenoson. Patients administered regadenoson had better tolerability and no severe event rates. Seventy percent of patients said that regadenoson produced fewer side effects compared to adenosine.

“Compared to adenosine, regadenoson had a similar image quality, fewer side effects and was better tolerated by patients,” Abbott said. Regadenoson can also be infused with low-level exercise.

“Pharmalogical stress agents have similar safety and efficacy as exercise stress,” Abbott concluded. “The addition of low-level exercise will also improve tolerability."